2003 Suburban lean codes

Joined
Nov 17, 2006
Messages
4,478
Likes
6
Points
38
Location
Portland,Oregon
#1
2003 Chev Suburban.2wd..5.3 VINZ...flex fuel..I think I am looking at a bad fuel pump, but wanted to get some input on this...It runs fine, but the idle fluctuates between 400 & 800 rpm at idle...Pulled 2 codes...PO171 & PO174...system to lean.. bank 1 & 2....The fuel filter was just changed and they had the fuel system flushed....but it didn't help so now I have it..Fuel PSI says it should be 48-54 PSI...KOEO is 42 PSI and when I turn it off it holds pressure for quite awhile..there is no fuel in the FPR vacuum hose...When I put my scanner on it the short term fuel trim is about 51.5% at idle and fluctuates a little...the long term fuel trim sets at 25.0% and never changes..I am not sure how to read it..When it is idling the fuel pressure stays at 42 PSI....any ideas greatly appreciated...I hope I didn't forget anything......Jim
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
9,904
Likes
180
Points
63
Location
St-Hyacinthe, Quebec, Canada
#2
Hey jim, can you get a vacuum gauge on this, I don't like the odds of both a up and down idle and two banks lean. How is your vacuum reading on this? Is the truck in your great looking shop right now? If so should be a real hassle to get that reading. I'll hang around then go from there. Short trim looks to be enriching confirming a lean condition, just want to take vacuum out of my mind before going for a fuel p test
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
9,904
Likes
180
Points
63
Location
St-Hyacinthe, Quebec, Canada
#3
You can pinch the fuel return on this engine, you may notice a difference if you have a bad pump, will cause fuel pressure to increase a bit changing that +50% fuel trim. At this much fiel trim that engine is starved right now. I would check for cracked air ducts, air filter way overdue, exhaust leaks before o2 sensor, things that can affect that fuel trim.
 

billr

wrench
Staff member
Joined
Mar 12, 2007
Messages
6,498
Likes
83
Points
48
#4
Flex-fuel makes me wonder a bit how that sensor can be checked. Obviously, the mixture has to change dramatically between pure gasoline and E85. I expect they do that by changing injector pulse-width, can you read those? Just some things to consider, with the FP pressure seeming to be low the pump is probably the problem. Or the FPR, they can be bad without the diaphram leaking.
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
9,904
Likes
180
Points
63
Location
St-Hyacinthe, Quebec, Canada
#5
Yeah bill, I got jim in PM, and he is checking some stuff out probably as we speak, just want to eliminate the obvious before ripping down a tank.
 
Joined
Nov 17, 2006
Messages
4,478
Likes
6
Points
38
Location
Portland,Oregon
#6
OK....I put a vacuum gauge on it...it is steady at 18in. vacuum.....I thought I was hearing a vacuum leak, so I sprayed some brake cleaner.......and could hear it sucking air....It has a vacuum leak around the EVAP canister purge solenoid ...see pic......if I wiggle it....it really leaks...I don't know if it is loose or broke....but definitely leaking...is that enough to cause my codes and the idle problem?...Jim

[attachment deleted by server]
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
9,904
Likes
180
Points
63
Location
St-Hyacinthe, Quebec, Canada
#7
You bet Jim, that's why I asked, the symptoms were just to odd to be a pump. More a vac leak, glad you got it pinned down. I am a smiling cat now!!
 
Joined
Nov 17, 2006
Messages
4,478
Likes
6
Points
38
Location
Portland,Oregon
#8
I will pull it off and see if it is just loose or if maybe somebody leaned on it and broke it....I know they had it worked on someplace before it came here and it sits right on top...maybe somebody leaned on it and broke it......I will post back when I find out...Jim
 
Joined
Nov 17, 2006
Messages
4,478
Likes
6
Points
38
Location
Portland,Oregon
#9
OK....I pulled the EVAP canister purge solenoid and it was cocked and not down in the hole but was OK...I put it back on right and now the idle is steady and the short term fuel trim is between -2.0 and a -4.0...The long term fuel trim was doing about the same as the short term and then kind of settled at 25%....the fuel pressure while running was still sitting on 42psi and I pulled the vacuum line to the fuel pressure regulator and the fuel pressure goes to 50psi with the line disconnected...but at least the idle is OK now and that was what he was worried about....so is the pump maybe starting to go bad or what?....Jim
 
Joined
Nov 17, 2006
Messages
4,478
Likes
6
Points
38
Location
Portland,Oregon
#10
OK....I let it run for awhile...no codes and the idle is still OK.....The short term fuel trim is around 0%....moves a little and the long term is sitting at 15% steady....Jim
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
9,904
Likes
180
Points
63
Location
St-Hyacinthe, Quebec, Canada
#11
i would not be to finicky with that fuel pressure. The idle returned to normal, fuel trim is beautiful,15% is ok for ethanol, if it was plain ole gas I would want -10 to +10 ranging back and forth signifying the o2 sensors are correcting and reading map, baro etc. Good job Jim, that was aa quick fix for a real complex DIY job, but you are a pro. This thread will help others for sure down the line, they will see how two pro's went down a logic path. In our case the logic path was arrived at real quick because of easy symptoms and readily available tools. Again, good fixed

Edit, was thinking, if that LTFT continues to always stay in the +15%, that may be an indicator of a future failing pump, might want to ask your buddy if he wants you to change it, If you want to do that job. Don't know your dispositions. If you were close to me I would have said sen him over if you don't want the job. Beside the point. Anyways, if that LTFT doesn't go negative sometimes, it is indicating a constant lean condition and you had effectively two separate problems on this truck, IMHO.
 
Joined
Nov 17, 2006
Messages
4,478
Likes
6
Points
38
Location
Portland,Oregon
#12
Thanks nick....I will have the truck all day tomorrow...they aren't going to pick it up till late...so I am going to drive it around some and watch the fuel trims and make sure the CEL doesn't come back on...Jim
 
Joined
Nov 17, 2006
Messages
4,478
Likes
6
Points
38
Location
Portland,Oregon
#13
fixed...........Hey Nick and Bill....thought I would let you guys know that the truck is fixed and gone home to the owner......The purge solenoid leaking was the problem....I drove it around for awhile the next day with the scanner hooked up and the fuel trims got better...the one was around 0...+ or - a little and the other would do the same thing except once in awhile would go back to the +15 or so......I told her we might need to do a fuel pump in the near future and she said she will drive it till the gas tank is pretty low and then bring it in and let me change it...thanks for all the help on this....Jim
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
9,904
Likes
180
Points
63
Location
St-Hyacinthe, Quebec, Canada
#14
Let this be a lesson to all the ppl hat have scanners which display Fuel trim data, this is a great information to look at when diagnosing lean and rich conditions. Good also for isolating misfires for ignition or fuel, tells you which system is affected without not so much as just hooking it up. Fuel trims are awesome data to look for when buying a scanner, a must have if your considering a scanner.